Gas turbines airfoils such as nozzles are subjected to intense heat and external pressures in the hot gas path. These rigorous operating conditions are exacerbated by advances in the technology, which may include both increased operating temperatures and greater hot gas path pressures. As a result, gas turbine nozzles are sometimes cooled by flowing a fluid through a manifold inserted into the core of the nozzle, which exits the manifold through impingement holes into a post-impingement cavity, and which then exits the post-impingement cavity through apertures in exterior wall of the nozzle, forming a film layer of the fluid on the exterior of the nozzle.
However, flowing the fluid through the manifold in a sufficient volume to cool the entire nozzle decreases efficiency of the gas turbine due to the need to maintain a sufficiently high back-flow margin (post-impingement pressure relative to the gas path pressure) at every external aperture, and to overcome crossflow in the post-impingement cavity. Attempts to divide the post-impingement cavity for better flow control have been inhibited by significant fluid leakage between sub-divided portions at operating conditions, and further, sub-dividing structures may be adversely affected by differential heat expansion and mechanical stresses from turbine operation.